Unit4_AnzaiM

Unit 4: Electricity
Basic Terminology:
The structure of the atom helps us understand how electricity works.
Charge Interactions:
There are basic laws that explain the characteristics of electricity.

Conductors and Insulators:
Conductors are materials that allow the transfer of electrons freely. A perfect conductor would cause no interference with the movement of electrons, but conductors cannot have no interference.
Insulators are materials that disable the transfer of electrons. A perfect insulator would disallow any movement of electrons through the material.





















Polarization:
Polarization is the act of inducing electrons and protons to move in a certain matter through the reactions of the law of electricity.
The electrons move towards positive objects and the protons move towards negative objects.


















Methods of Charging:
Charging by Friction - The action of moving two objects against each other causes the attraction of the electrons in one material to another object causing attraction of the protons in one and electrons in another object. We can see this phenomenon with the classic balloon and hair trick which causes the hairs to stand up when a balloon is rubbed on the head.

Law of Conservation of Energy: The law of conservation states that when two objects transfer charge, they have no change in overall net charge because it always remains 0. The electrons are transferred to one object while the other loses electrons. When the two objecs are compared against each other they are at equilibrium. This is why the law of conservation of energy works.

Charging by Induction: This is a method that charges objects without physical interaction with the object.

As shown in the diagram, the spheres are not actually touching the balloon, but they are recieving a change in charge because the electrons and protons are moving according to their affinity with the object with charge. When finished and taken apart they two spheres have different charges.












Like the previous diagram we can experience the same effect with an object of positive charge. The same essential movement of electrons is occuring.

We can also ground charge from these spheres and cause a change in charge with one sphere and a hand.











Charging by Conduction:
Charging by conduction is the movement of charge due to physical contact of charged and uncharged objects.












The diagram above shows the movement of electrons because of an excess of charge in the metal sphere. When the metal sphere touches the electroscope the electrons move quickly into the electroscope because of the excess in charge.

Grounding:
Grounding was discussed briefly in the induction section, but is a very important factor in electricity for our everyday usages.
Grounding is the transfer of an excess of charge because of affinity into the ground where the charge is neutralized.
It is said that the earth has too great of mass to become charged or imbalanced.













Charge Interactions:
Charge interactions have 3 variables, distance, charge(object one), and charge(object two).
These 3 variables cause objects to acquire electrical force that either repel or attact.
The forces are expressed as vector quantities so they require both direction and quantity.

Coulomb's Law:
We can use the three variables in an equation find the total force of an interaction.



This is coulomb's law where k is a constant of 9 x 10^9
Q1 is charge of one object
Q2 is the charge of a second object
d is the distance between the objects.

Action at a Distance: AKA electric fields
As we see when charged objects such as a balloon over bits of paper attract to each other without every physically coming into contact, we can explain the action at a distance phenomenon by understanding that there is an electric field surrounding these charged objects.

When we calculate electric field we consider the electric field strength to be in terms of force per charge ratio. This ratio is able to show the strength and magnitude of the electric field.




If the electric field strength is denoted by the symbol E, then the equation can be rewritten in symbolic form as
.


Electric Field Lines:
As well as how we can express electric fields mathematically and quantitatively we can express electric fields visually with diagrams of the interaction of charges.

For the use of diagrams when expressing charges, we have general rules that we have to follow.
The first rule is that density and amount of lines expresses the magnitude of the charges.









The second rule states that the lines are perpendicular to the surface of the point where it leaves the source.
The final rule states that the lines may not intersect when it is drawn from the source.

Cool Animation:


Electric Potential Difference:
Electric Potential:

• 1) Electric charge - a property of the object experiencing the electrical field, and 2) Distance from source - the location within the electric field
• 

The electric potential difference is expressed by the change in electric potential due to the change in position of an object. This change in position causes changes in potential of the electrical force.




It can be expressed as the change of electric potential in different locations.

Electrical Current:
An electrical current is a cyclic movement of electrons through a given circuitry.
Circuit is a closed loop in which electrons can flow continuously.
As we saw in the labs, the electric circuit shows that there is a constant current or flow because the bulb would be lit up constantly.









Requirements of a Circuit:
There are two requirements for a circuit to work.
1. The circuit must be closed and conducive.
2. There must be an energy source that moves the electrons opposite the electric field forces.

Electric Current:
Expressing electric current can be as simple as saying there are electrons moving through the wires of the circuit.
Physically speaking current can be expressed numerically and calculated.
Like other ratio quantities in physics such as power, velocity and acceleraiton current is a ratio value.
Current can be expressed with this equation:




Current expresed as I are in units of amperes. amperes = coulombs / time.

Conventional Current Direction:












The current moves from the positive to the negative moving against the electric field.

Important Facts about Current:
Current is very slow, but is present everywhere and is very dense. When current is present there is a constant steady flow of electrons everywhere within the cicuit which causes a fast reaction when things such as lights are turned on.

Power Putting Charges to Work:
When an electrical current is created without any load (A factor within circuitry that creates a more useful energy type) there would be short circuiting. Short circuiting is simply a problem that occurs because the electrical current moves too quickly, and drains energy quickly.

Power is the same as its usage in work but is a different factor.




Like mechanical power, the unit of electrical power is the watt, abbreviated W. (Quite obviously, it is important that the symbol W as the unit of power not be confused with the symbol W for the quantity of work done upon a charge by the energy source.) A watt of power is equivalent to the delivery of 1 joule of energy every second. In other words:1 watt = 1 joule / second

Electrical Resistance:
Electrical Resistance is caused by many factors.
Whether it be the length of the wire, load, or material there are many factors that causes resistance.

Material	Resistivity(ohm•meter)
Silver	1.59 x 10-8
Copper	1.7 x 10-8
Gold	2.4 x 10-8
Aluminum	2.8 x 10-8
Tungsten	5.6 x 10-8
Iron	10 x 10-8
Platinum	11 x 10-8
Lead	22 x 10-8
Nichrome	150 x 10-8
Carbon	3.5 x 105
Polystyrene	107 - 1011
Polyethylene	108 - 109
Glass	1010 - 1014
Hard Rubber	1013

The standard metric unit for resistance is the ohm, represented by the Greek letter omega - . An electrical device having a resistance of 5 ohms would be represented as R = 5 . The equation representing the dependency of the resistance (R) of a cylindrically shaped conductor (e.g., a wire) upon the variables that affect it is
where L represents the length of the wire (in meters), A represents the cross-sectional area of the wire (in meters2), and represents the resistivity of the material (in ohm•meter).

Ohm's Law:
V = I • R
In words, the electric potential difference between two points on a circuit (V) is equivalent to the product of the current between those two points (I) and the total resistance of all electrical devices present between those two points (R).

The Ohm's law equation can be rearranged and expressed as




Circuit Diagram:

circuit_diagram.jpg

Circuit_symbol.jpg

Circuit can be described as word and image. For the battery and single cell, the longer line refers the positive terminal.

Two Types of Conncetions:
Series Circuits:
Series Circuit is a type of connection that has only one line that traverses the external circuit.
Only one pathway exists. If one of the resistors breaks the entire line will turn off.












Using the diagram above we can figure out a general mathematic equation that we can use. Ibattery = I1 = I2 = I3 = Vbattery / Req

Parallel Circuits:
Parallel branches from the circuit with multiple segways or branches with different pathways.
Although there are many branches, the overall current remains the same.
(1/equivalent resistance) = (1/resistance of resistor 1) + (1/resistance of resistor 2).....























Combination Circuit:
The combination circuit is the same just combined two types of connections.
Cool Animation:

Replacement Labs:
Name: Masato Anzai


Student Exploration: Circuits


Vocabulary: ammeter, circuit, current, electron, ohmmeter, Ohm’s law, parallel circuit, resistance, resistor, series circuit, voltage


Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
Strings of holiday lights can be designed in one of two ways. In some strings of lights, each light is connected to the others along a single wire (in series). In others, each light is attached to its own wire (in parallel).

1. Suppose a single light bulb burns out. How do you think this will affect lights that are strung along a single wire? The rest of the bulbs will turn off

1. How will a single burned-out bulb affect the string of lights if each light is attached to its own wire? It won’t have an effect on the other lights

Gizmo Warm-up
The Circuits Gizmo™ shows a circuit board and a variety of components. Create a circuit with a battery, a light switch, a wire, and a light bulb, as shown. (Click the light switch to turn it to OFF.)

1. Click the light switch to turn it to ON. What happens? The light bulb turns on

1. Turn on Show current and select Electron flow. The moving dots represent a current of electrons—tiny, negatively charged particles—moving through the wire. Voltage is a measure of how much more potential energy an electron at one end of a battery has than an electron at the other end of the battery.
2. . How does changing the battery’s voltage affect the current? The current gets more electrons and movement.
3. How does changing the battery’s voltage affect the brightness of the light? The light becomes brighter.

1. Remove the wire. What happens? The light turns off.

Activity A: Ohm’s law

Get the Gizmo ready: Click Clear. Create the circuit shown at right. (Use the 10 ohm resistor.) Click on the battery. Set the Selected battery voltage to 10 volts.

Introduction: Resistors are devices that slow the flow of current in a wire. The resistance of the circuit to current is measured in units called ohms.

Question: What is the relationship between voltage, current, and resistance?

1. Form hypothesis: How do you think increasing the resistance in a circuit will affect the current in the wire? Over all flow of electrons becomes slower as resistance increases.
2. Observe: Turn the light switch On to start the flow of current. An ammeter is a device that measures current in Amperes (A). Drag the Ammeter () to various parts of the circuit.

1. Is the current the same throughout, or does it change? It is the same throughout.

1. What is the current in the wire now? 0.1 amperes

1. Collect data: Measure the current in the circuit using the resistor and voltage combinations given below.

Voltage	Resistance	Current
10 volts	10 ohms	1
20 volts	10 ohms	2
30 volts	10 ohms	3

Voltage	Resistance	Current
50 volts	20 ohms	2.5
50 volts	100 ohms	0.50
50 volts	200 ohms	0.25

1. Analyze: What is the mathematical relationship between voltage (V), resistance (R), and current (I)? Express your answer as an equation: I = V / R

This equation is known as Ohm’s law.

1. Test: Test your equation with other combinations of voltage and resistance. Modify the equation if necessary.

1. Apply: Use Ohm’s law to find the resistance of the light bulb in the Gizmo. What is it?

10 volts / 10 ohms * x = 0.67 x = 1.492 ohms
_

Activity B: Series circuits

Get the Gizmo ready: Click Clear. Create a circuit as shown. Click the battery to select it. Set the Selected battery voltage to 10 volts.

Question: In a series circuit, there is only one path for charge to flow. What are the properties of series circuits?

1. Observe: Turn the light switch ON and observe the light bulb. Then start replacing the wire segments with new light bulbs.

1. How does each new light bulb affect the others? It makes the other light bulbs dimmer
2. Use the Ammeter to measure the current in various parts of the circuit. Is the current the same throughout, or does it change? It is the same.

1. Form hypothesis: How do you think the total resistance of a series circuit is calculated?

It is added with each other.

1. Experiment: Create a series circuit with a 10-volt battery and four 10-ohm resistors, as shown. Measure the current.
2. Based on the voltage and current, what is the resistance of the circuit? (Hint: Use Ohm’s law.) 40ohms
3. Ohmmetersmeasure resistance. Remove the battery and attach the terminals of the Ohmmeter () to the ends of the circuit. What is the resistance? 40ohms
4. Make a rule: How do you calculate the total resistance of a series circuit? Add all resistance together.

Test your rule using the Gizmo. If necessary, modify your rule.

1. Extend your thinking: Replace the battery. Turn on Show current, and remove one resistor. Why would it be a problem if your household appliances were connected in a series circuit?

If one of the resistors broke, it would cause all other appliances to turn off.

Activity C: Parallel circuits

Get the Gizmo ready: Click Clear. Create a circuit as shown. Click the battery to select it. Set the Selected battery voltage to 15 volts.

Question: In a parallel circuit, there is more than one path along which charges can flow. What are the properties of parallel circuits?

1. Observe: Turn the light switch ON and observe the light bulb. Then add two more light bulbs to the circuit, parallel to the first two.

1. How does each new light bulb affect the others? Slightly dimmer
2. Use the Ammeter to measure the current in various parts of the circuit. Is the current the same throughout, or does it change? Explain: The current is half

1. Form hypothesis: How do you think the total resistance of a parallel circuit is calculated?

Resistance is calculated as 1/R

1. Experiment: With the battery voltage set to 15 volts, measure the current in a parallel circuit with 1, 2, 3, and 4 light bulbs. (In each case, place the ammeter next to the battery.) Use Ohm’s law to calculate the total resistance of the circuit. Record results below.

Number of light bulbs	1	2	3	4
Voltage	15 volts	15 volts	15 volts	15 volts
Current	2 amp	4amp	6amp	8amp
Total resistance	0.01	0.02	0.03	0.04

1. Make a rule: How would you find the resistance of a parallel circuit with n identical resistors?

Resistance = 2n

1. Apply: What will be the total resistance and current in a parallel circuit with a 15-volt battery and three 10-ohm resistors? Test your answers with the Gizmo.

Total resistance: 0.03 ohms Current: 6amperes
(Activity C continued on next page)

Activity C (continued from previous page)

1. Extend your thinking: Household appliances are usually connected in a parallel circuit. Why do you think it might be a problem if too many appliances are turned on at once? (Hint: current in a wire also produces heat.)

There would be too much heat because some of the appliances would have different resistance.

1. Calculate: Determining the total resistance of a parallel circuit when there is a variety of resistors is more complex.

• The total current in the circuit (I) is equal to the sum of currents in each branch:

• Ohm’s law (V = IR) can be rewritten as I = V / R. Substituting this expression into the equation above:

• (Note: Since each branch of the circuit might have a different resistance, we write R1, R2, and so forth. But the voltage is the same across each branch, so V is used for each term.)
• Divide each side of the equation by V, and you get an expression for the total resistance of the circuit:

1. Practice: Determine the total resistance of each of the following parallel circuits. Then use the Gizmo to check your answer. (You can calculate the total resistance from the current and voltage using Ohm’s law, or use the Ohmmeter to measure the resistance directly.)

1. A parallel circuit with a 20-ohm resistor and a 10-ohm resistor. 6.7ohms
2. A parallel circuit with two 20-ohm resistors and a 10-ohm resistor. 5ohms

1. A parallel circuit with a 15-ohm light bulb and a 20-ohm resistor. 8.3ohms
2. A parallel circuit with two 100-ohm resistors and a 20-ohm resistor. 14.3ohms
3. A parallel circuit with a 10-ohm, 20-ohm, 100-ohm and 200-ohm resistor. 6.06 ohms

Replacement Lab:

Name: Masato Anzai

Student Exploration: Circuit Builder


Vocabulary: circuit, closed circuit, conductor, current, fuse, insulator, open circuit, parallel circuit, series circuit, short circuit


Prior Knowledge Questions (Do these BEFORE using the Gizmo.)

1. What do a light bulb, a toaster, a radio, and a computer all have in common?

Closed circuit, fuse

1. Suppose you connect a battery to a small light bulb with a single wire. What do you think will happen? Explain your answer.

It will not function because it is not a complete circuit


Gizmo Warm-up: Build a circuit

1. Using the Standard components in the upper left of the Gizmo™, try to get a light bulb to light up! You can drag as many bulbs, wires, batteries, switches and fuses as you like onto the circuit board.

A circuit is a path containing easily moveable charges. When the light bulb lights up, charges (electrons) are flowing through the wire and light bulb. This flow of charge is called current.

1. Now try to light the bulb with the smallest number of components.

Make a sketch of your simple circuit in this space:

1. Based on what you have seen, what must be true for a circuit to light a bulb? The circuit must be closed incorporating the light bulb within the circuit

Activity A: Closing a circuit

Get the Gizmo ready: Click Clear. Turn on Show current. (Current is represented by moving arrows.) Set up components as shown to the right.

Introduction: You should have just built an open circuit (shown above). The gap on the left prevents the flow of charges. There are no gaps in a closed circuit, so charges flow.

Question: What materials will close a circuit?

1. Predict: Conductors are materials with easily movable charges, allowing electrical current. Insulators do not have easily movable charges, so current is not easily produced. Look at the nine Materials at lower left. Which do you think are conductors? Which are insulators?

1. Predicted conductors: Silver
2. Predicted insulators: Wood

1. How could you use your open circuit to test if a material is a conductor or insulator?

By including the material directly into the circuitry

1. Experiment: Drag each material into the gap of the open circuit. If the light bulb lights, the material is a conductor. If not, the material is an insulator. Keep track of your findings below.

Conductors	Insulators
Iron	Plastic
Silver	Wood
Brass	Glass
Copper	Yarn
lead

1. Analyze: Look at your list of conductors.
2. What kind of material are most conductors? Metals
3. Did any conductor have a different effect on the light bulb than the others? Explain.

Some allowed less resistance while others slowed things down.

Activity B: Series circuits

Get the Gizmo ready: Click Clear. Check that Show current is on. Build the circuit shown to the right.

Question: In a series circuit, components are arranged in a single loop. What are the characteristics of series circuits?

1. Observe: Turn the switch to ON, which allows charges to flow through the circuit. Notice how brightly the bulb is lit and how much current (shown by the arrows) there is. Now start replacing wire segments with light bulbs. You can fit up to four bulbs in this series circuit.

1. What do you notice about the brightness of the bulbs as you add more bulbs?

Lowered brightness as more bulbs are added.

1. Do all the bulbs have the same brightness? Yes
2. Look at the current arrows in each part of the circuit. Are there any parts of the circuit that have more current than other parts? No

1. Explore: Now remove a light bulb from your series circuit, leaving a gap. What happens to the remaining bulbs? Turns off
2. Extend your thinking: Build another series circuit with several light bulbs, a 1.5-volt AA battery, and at least a few wire segments. Turn the switch to ON.

1. How does a circuit with a 1.5-volt battery compare to a circuit with a 9-volt battery?

It can’t light the bulbs.

1. Replace one of the wire segments with another 1.5-volt battery. What happens?

The bulbs get brighter

1. Compare: Compare a series circuit powered by six 1.5-volt batteries to a series circuit powered by a single 9-volt battery. Make sure there are equal numbers of light bulbs in each circuit and that the batteries are all in the same orientation.

What do you notice? Difference in brightness
Why is this true? The changes in brightness is caused by difference in voltage which causes lower current.

Activity C: Parallel circuits

Get the Gizmo ready: Click Clear. Check that Show current is on. Build the circuit shown to the right.

Question: In a parallel circuit, there is more than one path that current can take. What are the characteristics of parallel circuits?

1. Observe: Turn the switch to ON, which allows charges to flow through the circuit. Notice how brightly each bulb is lit and how much charge is flowing in each part of the wire.

Are the two bulbs equally bright? Yes

1. Experiment: Add two more light bulbs to the circuit, as shown to the right. Turn the switch to ON, and observe the brightness of the bulbs.

1. Did the brightness of the bulbs change? Yes
2. Remove one light bulb. What happens? Slightly Brighter
3. How did the parallel circuit respond differently to these changes than a series circuit?

Adding bulbs: little change in brightness
Removing bulbs: little change in brightness

1. Observe: Replace one of the light bulbs in your circuit with a wire. Now there is a path in the circuit with no light bulb to slow down the moving charges. What happens?

It doesn’t move into the light bulbs because electrons want to move in a path with least resistance.
This situation is called a short circuit. The red arrows indicate enormous current. This is very dangerous because so much current will heat up the wire and could even start a fire!

1. Apply: Short circuits can be avoided using fuses, devices that melt if too hot. Set up the circuit shown to the right, and turn the switch ON.
2. What happens? Nothing
3. Create a short circuit. What happens now? The fuse breaks leaving no path
4. How does a fuse make the circuit safer? ­It destroys the short circuit when it occurs

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